The intent of the present project is to exploit the self-catalyzed prosthetic heme alkylation associated with xenobiotic metabolism to characterize the mechanism and the active site of cytochrome P-450 enzymes. In addition, the toxicological consequences of cytochrome P-450 inactivation, and its possible utility in the case of isozyme-specific agents, is also to be examined. Experiments are proposed to: (a) determine where in the catalytic sequence heme alkylation diverges from metabolite formation, (b) define the role of free radicals in heme alkylation, and the importance of radical cation intermediates in normal catalysis by cytochrome P-450, (e) outline the topology of the active site of these enzymes, (f) develop isozyme-specific suicide substrates for cytocchrome P-450, particularly for isozymes involved in lipid metabollism, (g) clarify the inhibition of heme adducts with heme biosynthetic enzymes.